How to Increase the Maximum File Upload Size in WordPress

Update your .htaccess with the following line (note these figures are wildly exagerated and should be amended for your site).

php_value upload_max_filesize 25600M
php_value post_max_size 25600M
php_value max_execution_time 30000
php_value max_input_time 30000

Should the above fail, you can add the following to your functions.php

@ini_set( 'upload_max_size' , '64M' );
@ini_set( 'post_max_size', '64M');
@ini_set( 'max_execution_time', '300' );